1. Field of the Invention
The invention relates generally to the field of photography, and in particular to a film cassette containing roll film. More specifically, the invention relates to a film cassette that is capable of automatically advancing a non-protruding film leader out of the cassette shell responsive to unwinding rotation of a film spool inside the shell.
2. Description of the Prior Art
A 35mm film cassette has been proposed which, unlike conventional film cassettes, can be operated to automatically advance a film leader out of the cassette shell simply by rotating the film spool in the unwinding direction. The film leader originally is located entirely inside the cassette shell. Specifically, in commonly assigned U.S. Pat. No. 5,046,682, granted Sep. 10, 1991, there is disclosed a film cassette wherein a spool is supported for rotation in an unwinding direction inside a cassette shell, a filmstrip is coiled about the spool to form a film roll with an outermost convolution that is a non-protruding leader, a pair of flanges are coaxially arranged along the spool to radially confine the film roll to keep the roll captive, and a film stripper is located substantially adjacent a passageway to the exterior of the shell to be received between an inclined leading edge of the leader and a next-inward convolution of the film roll to divert the leading edge into the passageway when the spool is rotated in the unwinding direction. Once the inclined leading edge is substantially advanced into the passageway, the transverse stiffness of the filmstrip serves to flex the flanges away from each other to permit the filmstrip to escape the confinement of the flanges.
If the film roll has been stored on the spool for an unduly long time, it may develop what is commonly referred to as a "core set". The core set, in essence, manifests itself as a lack of resistance of the film roll to being curled inward about the spool. Consequently, when the spool is rotated in the unwinding direction to move the inclined leading edge of the leader over the stripper, a certain portion of the leading edge not yet advanced over the stripper may sag into a space between the outermost convolution of the film roll and the entrance to the passageway. Since the leader has a core set, it might remain in the space and cause a film jam inside the cassette shell.